Predictions for BAO distance estimates from the cross-correlation of the Lyman-α forest and redshifted 21-cm emission

Abstract

We investigate the possibility of using the cross-correlation of the Lyman-α forest and redshifted 21-cm emission to detect the baryon acoustic oscillation (BAO). The standard Fisher matrix formalism is used to determine the accuracy with which it will be possible to measure cosmological distances using this signal. Earlier predictions [1] indicate that it will be possible to measure the dilation factor DV with 1.9% accuracy at z = 2.5 from the BOSS Lyman-α forest auto-correlation. In this paper we investigate if it is possible to improve the accuracy using the cross-correlation. We use a simple parametrization of the Lyman-α forest survey which very loosely matches some properties of the BOSS. For the redshifted 21-cm observations we consider a hypothetical radio interferometric array layout. It is assumed that the observations span z = 2 to 3 and covers the 10,000 deg2 sky coverage of BOSS. We find that it is possible to significantly increase the accuracy of the distance estimates by considering the cross-correlation signal.